The present invention relates to a filtration system releasably attachable to a blower wheel in an HVAC system, and in particular, to a filter cartridge having a plurality of compartments containing a filter medium and a plurality of substantially unimpeded air flow passages that maintain a high flow rate even when the filter medium is in a fully loaded state.
With increased concern over environmental air quality, innovative solutions have been sought for adding filtration capacity to new and existing air circulation systems, such as heating, ventilation, and cooling systems (HVAC) for buildings and vehicles. For example, the HVAC systems in most vehicles do not include air filters. Minimal space is generally available for retrofitting a filter to the HVAC system. Moreover, it may be necessary to provide one filter for incoming air and a second filter for air recirculating within the passenger compartment. Even on new vehicles, space within the HVAC system is at a premium and it is difficult for some manufacturers to provide a location for an appropriate filter.
In addition to the difficulty of finding sufficient space for a filter, the failure mode of most filter media also raises concerns. Over time, environmental contaminants accumulate in filters, typically resulting in a reduced flow rate through the air circulation system. Failure to replace the filter media periodically can result in an increased static air pressure drop across the filter and reduced efficiency for the air circulation system. The reduced flow rate through a loaded filter can also create safety hazards, such as allowing insufficient airflow for operating the defrost system of an HVAC system.
One approach to retrofitting an air filter to an HVAC system of a vehicle is disclosed in U.S. Pat. No. 5,683,478 (Anonychuk). The air filter is sized and shaped to fit into a cavity located within a blower motor assembly. An outwardly extended lip is provided on the base of the air filter for rigid attachment to a rim located below the fan on the automobile. The fan in the blower motor assembly rotates around the stationary filter. Although the ""478 patent recognizes the need to provide filtration efficiency without impeding airflow, air flow will inevitably be reduced as the filter becomes loaded with environmental contaminants. The failure mode of the filter element may be an unacceptable reduction in airflow through the blower motor assembly.
U.S. Pat. No. 5,265,348 (Fleishman et al.) discloses the use of a rotating foam material on a rotary fan to reduce noise.
Various filters for blower wheels are disclosed in commonly assigned U.S. patent applications Ser. No. 09/126,189 (now U.S. Pat. No. 6,099,608, issued Aug. 8, 2000), entitled Filtration System for HVAC Applications; Ser. No. 09/126,190 (now U.S. Pat. No. 6,099,609, issued Aug. 8, 2000), entitled Moving Sorbent Filter Device; and Ser. No. 09/126,181 (now U.S. Pat. No. 6,102,988, issued Aug. 15, 2000), entitled Moving Filter Device having Filter Elements with Flow Passages and Method of Filtering Air, all filed on Jul. 30, 1998.
The present invention is directed to a filtration system attachable to a blower wheel in an HVAC system. The present filtration system is particulary useful to provide cabin air filtration to vehicles, which currently do not have a filter designed in the HVAC system. Movement of the filter cartridge with the blower wheel increases filtration efficiency during blower operation. The present moving filter cartridge can be retrofitted to most existing blower wheels. The filter cartridge releasably attaches to either the outside perimeter or the inside perimeter of the blower wheel.
An advantage of the present filtration system is that it is retrofittable into most existing vehicles. Since most cars have a blower wheel, a space exists to place the present filter cartridge. On the other hand, it is not feasible to easily retrofit a vehicle with a conventional cabin air filter since little additional space is available. Locating the filter cartridge at the blower wheel provides filtration of both outside air entering the HVAC system and air being recirculated within the system. Most cabin air filters only filter the air as it enters the vehicle.
The present filter cartridge includes both compartments containing a filter medium and flow passages of a size, density and shape such that a high flow rate is maintained even when the filter media is fully loaded. The spinning action of the filter cartridge causes the filter medium contained in the compartments to impact air as it passes through the flow passages. Some loss of filtration efficiency due to the flow passages is offset by increased efficiency due to the movement of the filter cartridge with the blower wheel.
The filtration system rotates in conjunction with a blower wheel. The blower wheel has a plurality of fan blades arranged in a spaced relationship radially around a blower cavity. The blower wheel defines a flow path extending radially outward from the blower cavity and through the fan blades when the blower wheel is rotating. The present filtration system can reduce the airflow through the blower wheel, thereby reducing the power consumption of the motor. The relationship between power and flow is a cubic function. By reducing the load (i.e., power consumption), the life of the motor is extended.
In one embodiment, the filter cartridge comprises a mesh structure forming a generally annular cylinder comprising a center opening, a plurality of compartments containing a filter medium, and spaces between the compartments. The spaces between the compartments comprise substantially unimpeded airflow passages that permit airflow even when the filter medium is fully loaded.
The compartments may extend radially into the center opening. In one embodiment, the compartments comprise one of corrugations or pleats in one or more of the mesh layers. The compartments can be shaped to operate as fan blades. The compartments are typically discrete pockets. The mesh typically comprises an expanded metal screen. In one embodiment, a mesh material extends across a top opening of the annular cylinder. The filter medium can be selected from a group consisting of electret charged medium, particulate medium, sorbents medium, agglomerated carbon or combinations thereof.
The filter cartridge comprises at least one end cap. An air flow passage can optionally extend through the at least one end cap. The end cap can also include weight balancing cavities and/or removable weight balancing tabs.
In another embodiment, the filter cartridge comprises a first mesh layer having a plurality of raised portions and a second mesh layer engaged with the first mesh layer such that the raised portions comprise compartments. A filter medium is retained in the compartments. Spaces between the compartments comprise substantially unimpeded airflow passages that permit airflow even when the filter medium is fully loaded. The filter medium is preferably agglomerated carbon or other filter medium such as activated carbon or other sorbent materials that remove odors and gases from the air, such as diesel exhaust, car exhaust, urban or farm smells, carbon monoxide, and ozone.